Dengue vaccine found to worsen disease symptoms

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Photos:Dengue fever: How a mosquito infected millions

Dengue virus is carried by the Aedes aegypti mosquito, the same type that can spread Zika virus. A bite from a mosquito harboring the virus can result in headaches, rashes and severe joint pains. In serious cases, it can cause internal bleeding and death.

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Photos:Dengue fever: How a mosquito infected millions

There is no drug for dengue. Patients must be monitored carefully for the onset of the severe form of dengue. Pictured, a nurse looks after a patient with dengue at a hospital in Manila, Philippines.

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Photos:Dengue fever: How a mosquito infected millions

The main control measures for dengue to date have been to reduce the numbers of mosquitoes by large-scale spraying of insecticides. The chemicals have been deployed in both residential and public spaces in a mass culling of the insects spreading the disease.

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Photos:Dengue fever: How a mosquito infected millions

Urbanization has aided the spread of dengue, with more than 100 countries now endemic for the disease. Pictured, containers, bottles and tires are perfect breeding sites for Aedes aegypti mosquitoes that transmit the dengue virus. The versatile mosquitoes can lay eggs on any shallow surface of water.

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Photos:Dengue fever: How a mosquito infected millions

Public spraying of insecticides is based on seasonal changes, with more cases expected during rainy seasons in the tropics. But the measures haven't proven to curb the spread of disease adequately.

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Photos:Dengue fever: How a mosquito infected millions

Experts believe a vaccine is needed to truly control the disease. A dengue vaccine, called Dengvaxia, recently became available in Mexico, Brazil, the Philippines and El Salvador.

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Story highlights

The Philippines has halted a massive dengue fever vaccination effort

The country has launched an investigation into the approval of Dengvaxia

(CNN)The Philippines has suspended its large-scale dengue vaccination effort amid the surprising results of a new study conducted by the vaccine's manufacturer.

On Wednesday, French pharmaceutical giant Sanofi Pasteur published clinical trial data showing that its dengue vaccine, Dengvaxia, could have unintended consequences in patients who had never been infected with the mosquito-borne virus.

"The analysis confirmed that Dengvaxia provides persistent (protective) benefit against dengue fever in those who had prior infection," Sanofi said in a statement. "For those not previously infected by dengue virus, however, the analysis found that in the longer term, more cases of severe disease could occur following vaccination upon a subsequent dengue infection."

On Monday, Harry Roque Jr., a spokesman for Philippines President Rodrigo Duterte, announced that the Department of Justice would launch an investigation into the fast-track approval of Dengvaxia by the previous administration. Assistant Health Secretary Lyndon Lee Suy said his agency would work with the Department of Education to monitor all recipients of the vaccine for adverse health effects.

"We will leave no stone unturned in making those responsible for this shameless public health scam which puts hundreds of thousands of young lives at risk accountable," Roque said Sunday.

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In a statement, Sanofi said it would "continue to seek constructive and transparent dialogue" with the Food and Drug Administration of the Philippines.

More than 730,000 people in the Philippines have been vaccinated with Dengvaxia since April 2016, when the World Health Organization first recommended inoculating anyone 9 and older living in high-risk areas. Ninety percent had already had dengue, the country's Department of Health said.

In July 2016, the WHO published a paper that cautioned, "Vaccination may be ineffective or may theoretically even increase the future risk of (hospitalization) or severe dengue illness in those who are (uninfected) at the time of first vaccination."

Still, the vaccination campaign in the Philippines continued until last week.

Dengue is a viral infection transmitted by the Aedes aegypti mosquito, the same insect responsible for spreading Zika, chikungunya and yellow fever. The WHO estimates roughly half of the world's population is now at risk of contracting the virus and that 390 million people are infected every year. Only about 25% exhibit any symptoms.

Symptoms of dengue include high fever, headache and eye pain, as well as joint, muscle or bone pain, according to the US Centers for Disease Control and Prevention. The CDC says to "go IMMEDIATELY to an emergency room or the closest health care provider if any of the following warning signs appear": severe abdominal pain or persistent vomiting; red spots or patches on the skin; bleeding from the nose or gums; vomiting blood; "black, tarry" stools; pale, cold or clammy skin; or difficulty breathing.

The CDC says people who suspect that they have contracted dengue can take pain relievers with acetaminophen but to avoid medications containing ibuprofen or aspirin. "They should also rest, drink plenty of fluids to prevent dehydration ... and consult a physician."

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There are four "distinct, but closely related" strains of the virus that causes dengue, according to the WHO. Once someone recovers from an infection of one of the strains, they cannot become infected with that strain again. But the more times someone is infected with a different strain, the more likely subsequent infections are to result in "severe dengue."

While the review of Dengvaxia is carried out in the Philippines, Sanofi has proposed a "label update" to recommend that people who have never been infected with any strain of dengue not be vaccinated.